Air amount estimating apparatus for internal combustion engine with supercharger

Abstract

An air amount estimating apparatus in an internal combustion engine having a supercharger that estimates with high accuracy an amount of air drawn into a cylinder without involving an increased calculation load. The air amount estimating apparatus estimates a cylinder air amount through calculation that incorporates a physical model representing air flowing behavior through an intake path. When, at this time, a ratio of throttle downstream pressure to throttle upstream pressure as calculated with the physical model is smaller than a reference ratio, a throttle flow rate is calculated using an equation of throttle based on the throttle upstream pressure, the throttle downstream pressure, and a throttle opening. When the ratio of the throttle downstream pressure to the throttle upstream pressure is greater than the reference ratio, the throttle flow rate is calculated using a linear interpolation equation based on a compressor flow rate and an intake valve flow rate.

1 . An air amount estimating apparatus for a supercharged internal combustion engine having an intake path for introducing air drawn in from an outside into a cylinder, a compressor disposed in the intake path, a throttle disposed in the intake path downstream of the compressor, and an intake valve disposed at a connection between the intake path and the cylinder, the air amount estimating apparatus comprising:
 means for calculating a compressor flow rate, which is a flow rate of air passing through the compressor, based on a throttle upstream pressure, which is pressure of air in a throttle upstream section which is an intake path section from the compressor to the throttle, and based on a rotational speed of the compressor;   means for calculating the throttle upstream pressure using a physical model developed based on a conservation law of air in the throttle upstream section and based on the compressor flow rate and a throttle flow rate, which is a flow rate of air passing through the throttle;   means for calculating the throttle flow rate;   means for calculating a throttle downstream pressure, which is a pressure of air in a throttle downstream section which is an intake path section from the throttle to the intake valve, the means using a physical model developed based on a conservation law of air in the throttle downstream section and calculating the throttle downstream pressure based on the throttle flow rate and an intake valve flow rate, which is a flow rate of air passing through the intake valve;   means for calculating the intake valve flow rate based on the throttle downstream pressure; and   means for calculating an amount of air drawn into the cylinder based on the intake valve flow rate; wherein:   the throttle flow rate calculating means includes:   first calculating means for calculating the throttle flow rate using an equation of throttle based on the throttle upstream pressure, the throttle downstream pressure, and an opening of the throttle;   second calculating means for calculating the throttle flow rate using an equation of linear interpolation based on the compressor flow rate and the intake valve flow rate;   selection condition determining means for determining whether or not a predetermined selection condition is satisfied, the predetermined selection condition including a pressure condition that a difference between the throttle upstream pressure and the throttle downstream pressure is smaller than a reference difference or a ratio of the throttle downstream pressure to the throttle upstream pressure is greater than a reference ratio; and   selection means for opting to calculate the throttle flow rate using the first calculating means when the selection condition is determined not to be satisfied and opting to calculate the throttle flow rate using the second calculating means when the selection condition is determined to be satisfied.   
     
     
         2 . The air amount estimating apparatus for a supercharged internal combustion engine according to  claim 1 , wherein:
 the internal combustion engine includes an actuator for drawing air from the throttle upstream section to an outside or introducing air into the throttle upstream section from the outside; and   the throttle upstream pressure calculating means is configured to correct the throttle upstream pressure according as a flow rate of air in the throttle upstream section increases or decreases as the actuator operates.   
     
     
         3 . The air amount estimating apparatus for a supercharged internal combustion engine according to  claim 1 , wherein:
 the internal combustion engine includes an actuator for drawing air from the throttle downstream section to an outside or introducing air into the throttle downstream section from the outside; and   the throttle downstream pressure calculating means is configured to correct the throttle downstream pressure according as a flow rate of air in the throttle downstream section increases or decreases as the actuator operates.   
     
     
         4 . The air amount estimating apparatus for a supercharged internal combustion engine according to  claim 1 , wherein:
 the second calculating means is configured to calculate the throttle flow rate using an equation shown below, where m t  is the throttle flow rate, m cp  is the compressor flow rate, m c  is the intake valve flow rate, V us  is a volume of the throttle upstream section, and V ds  is a volume of the throttle downstream section,   
       
         
           
             
               
                 
                   
                     
                       m 
                       t 
                     
                     = 
                     
                       
                         
                           
                             V 
                             ds 
                           
                           * 
                           
                             m 
                             cp 
                           
                         
                         + 
                         
                           
                             V 
                             us 
                           
                           * 
                           
                             m 
                             c 
                           
                         
                       
                       
                         
                           V 
                           us 
                         
                         + 
                         
                           V 
                           ds 
                         
                       
                     
                   
                 
                 
                   
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         5 . An air amount estimating apparatus for a supercharged internal combustion engine having an intake path for introducing air drawn in from an outside into a cylinder, a compressor disposed in the intake path, a throttle disposed in the intake path downstream of the compressor, and an intake valve disposed at a connection between the intake path and the cylinder, the air amount estimating apparatus comprising:
 a calculating unit that calculates a compressor flow rate, which is a flow rate of air passing through the compressor, based on a throttle upstream pressure, which is pressure of air in a throttle upstream section which is an intake path section from the compressor to the throttle, and based on a rotational speed of the compressor;   a calculating unit that calculates the throttle upstream pressure using a physical model developed based on a conservation law of air in the throttle upstream section and based on the compressor flow rate and a throttle flow rate, which is a flow rate of air passing through the throttle;   a calculating unit that calculates the throttle flow rate;   a calculating unit that calculates a throttle downstream pressure, which is a pressure of air in a throttle downstream section which is an intake path section from the throttle to the intake valve, the calculating unit using a physical model developed based on a conservation law of air in the throttle downstream section and calculating the throttle downstream pressure based on the throttle flow rate and an intake valve flow rate, which is a flow rate of air passing through the intake valve;   a calculating unit that calculates the intake valve flow rate based on the throttle downstream pressure; and   a calculating unit that calculates an amount of air drawn into the cylinder based on the intake valve flow rate; wherein:   the throttle flow rate calculating unit includes:
 a first calculating unit that calculates the throttle flow rate using an equation of throttle based on the throttle upstream pressure, the throttle downstream pressure, and an opening of the throttle; 
 a second calculating unit that calculates the throttle flow rate using an equation of linear interpolation based on the compressor flow rate and the intake valve flow rate; 
 a selection condition determining unit that determines whether or not a predetermined selection condition is satisfied, the predetermined selection condition including a pressure condition that a difference between the throttle upstream pressure and the throttle downstream pressure is smaller than a reference difference or a ratio of the throttle downstream pressure to the throttle upstream pressure is greater than a reference ratio; and 
 a selection unit that opts to calculate the throttle flow rate using the first calculating unit when the selection condition is determined not to be satisfied and opts to calculate the throttle flow rate using the second calculating unit when the selection condition is determined to be satisfied.